<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
        <script>
            var foo1;
            function foo1() {
                alert('嘻嘻')
            }
            function foo1() {
                alert('嘻嘻')
            }
            function foo1() {
                alert('嘻嘻')
            }

            alert(foo1);

            foo1=10;

            alert(foo1);

            alert(foo1);


            alert(foo1);

        </script>
</body>
</html>